in the oceans. some forms of life flourish in this salty environment. but humans require an abundant supply of freshwater. less than 1% of all the earth's water is readily available for human consumption. in the semi-arid desert plains of the southwest united states, where rainfall averages just 2 1/2 centimeters per month, tom maddock studies this scarce resource. dr. maddock: the real problem that we have is that with increasing populations and shortages of water, we are becoming very vulnerable. in the southwest, there's a very unique vulnerability here, simply because where do we get the water if there is no water? narrator: across the country in northern florida, the quantity of water isn't an issue. rainfall averages an abundant 1 1/4 meters each year. wendy graham and her colleagues evaluate and model the impacts of industrial and agricultural land use threatening the world's largest collection of freshwater springs. dr. graham: right now, the biggest question is how far we can stress the system and not push it past the point of no return. narrator: both researchers are working towar

by running water are found in nearly every terrestrial environment on earth. they're even abundant in deserts, where sudden rainstorms and flash floods can produce more geomorphic change in a few hours than years of desert winds. but there would be no running water without slopes. land slopes are both created and maintained by tectonic activity. indeed, the shape of much of the earth's surface is the result of a constant competition between tectonic forces and the destructive effects of running water. nowhere is this duel between tectonism and running water easier to appreciate than here at the grand canyon, where the colorado river continues to sustain the evolution of one of the most beautiful and distinctive landscapes on earth. captioning performed by the national captioning institute, inc. captions copyright 1991 the corporation for community college television announcer: the bare necessities of living healthy are easy. just eat right, be active, and have fun. yeah! go to mypyramid.gov to find out more.

, it helps me see more in the natural environment, and hopefully, with a class like beliefs and believers, you get sensitized, you know, to seeing the issues that regard religion and beliefs and behavior out there. anybody else? >> yitzhak rabin said, during the israeli conflict with the palestinian- or the arabs, whatever- he said if he didn't know the bible very well, they never would have found the water holes, and he said, "if that's true, what about the rest of it?" >> yes, well said. i mean, that's what we talked about in one of our recent classes is the importance of biblical literacy, you know, at least in a country that seems to uphold it to such an extent. other comments, observations- things off the top of your head? >> this was in the wall street journal- you don't expect to find anything like this in the wall street journal- the title of it is, "praying is good medicine." and it's the story of a doctor who is sitting beside the bed of one of his patients and she is afraid that she's terminally ill, and so she asks him if he will pray with her, and he's so startled, he doesn't

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